An aluminum plated steel sheet for Hot Press Forming (HPF) is generally prepared by immersing a steel sheet having a high degree of hardenability in a plating bath containing a plating solution based on Al for plating, and then the plated steel sheet having an Al plated layer on the surface thereof is hot pressed. Such a steel sheet is widely used in the manufacturing of vehicle parts having complicated shapes and strengths of 1300 MPa or higher.
However, in the HPF heating process, the plated layer is composed of an alloyed layer comprising an intermetallic compound consisting of FeAl or Fe2Al5 and the like as an upper layer, and a diffusion layer consisting of Fe 80% to 95 wt % (hereinafter all steel ingredients are in wt %) as a lower layer. However, because the alloyed layer formed uppermost in the plated layer has brittleness as compared to the diffusion layer, the alloyed layer may be detached from the plated layer during hot press forming and may be attached to a pressing side. Therefore, this disadvantage makes continuous hot press forming difficult.
Namely, if the Al plated material is hot press formed by heating thereof in a heating furnace at a temperature of 900° C. to 930° C., the plated layer may be detached from a region of high surface friction, and at this time, an overall alloyed layer or a portion thereof may be detached from the region of high surface friction, and therefore, there may be a problem in that the detached plated layer may be attached to the surface of a hot press forming mold.
Thus, the development of an HPF part which can overcome the above-mentioned problems and have excellent press formability is required.